Microwave phase shifter



Aug. 4, 1953 J. F. ZALESKI MICROWAVE PHASE SHIFTER Filed Dec. 29, 1951 INVENTOR. JOHN F. .Z/PLEJK/ Patented Aug. 4, 1953 UNITED STATES PATENT OFFICE 2,647,950 MICROWAVE PHASE SHIFTER- John F. Zaleski, Valhalla, eral Precision Laborato poration of New York Application December 29, 1951, Serial N 0. 264,094 6 Claims. 333-9) This invention pertains to microwave phase shifters of the type used for changing the relative phase of microwave energy in two transmission lines.

In any microwave transmission line the transmission of energy is accomplished by means of an electromagnetic field guided by the line conductors, boundaries or walls and, since the energy follows the laws of wave motion, the interrelation of the electric and magnetic energy forms changes from point to point along the transmission line, this interrelation being termed the phase. Any transmission line device that eil'ectively adds or subtracts length from the transmission line thereby changes the phase of the microwave energy at any selected subsequent location, and this method is used to change or shift the phase of microwave energy.

In the instant invention the effective guide length is changed in an unique manner, and at the same time the applied microwave energy is divided into two exactly equal parts. That is, in this invention a phase shifter is combined with a power divider to form an instrument especially suitable for particular purposes. For example, the device of the instant invention is particularly useful for periodically changing the relative phase of microwave energy fed to two antennas, so that the two antennas will alternately emit energy in phase and 180 out of phase, their intensities of emission being the same in both cases. This result is advantageously accomplished by the invention because of its high eifieiency in the switched positions and because of the simplicity of the arrangement to produce a phase shift of precisely 180.

Briefly the invention provides a rectangular hollow guide to serve as a microwave energy input and a second rectangular hollow guide attached to the first guide to serve as a pair of outputs. A two-position switching arrangement is provided at the point of attachment of the two guides.

One object of this invention then is to provide a microwave hollow guide phase shifter that shifts the phase relation of two hollow microwave guide connections from a first value to a second'value.

Another object is to provide a combined phase shifter and power divider that divides input microwave power into two exactly equal output parts having a phase relation switchable by exactly 180, the losses in the switched positions being negligible. 7

Still another object is to provide a microwave phase switch that switches the e t e p se of N. Y., assignor to Genry Incorporated, a cortwo microwave energies from one value to another value without affecting the relative magnitude of the energies.

Further understanding of the invention may be secured from the detailed description and the associated drawings in which:

Figure 1 is a general view of a phase shifter embodying the invention.

Figs. 2 and 3 are cross-sectional views of Fig. 1 taken on the lines 2-2 and 3-3 respectively.

Referring now to Fig. 1, a rectangular hollow microwave guide iI short-circuited by a conductive plate I 2 at one end is arranged for excitation at the other or input end by microwave energy generated at I3. Another rectangular hollow microwave guide I4 of similar cross-sectional dimensions is joined at right angles to the of guide I4 but separated therefrom by the length of the box I6. The guide I4 is loaded at its two output ends or terminals I9 and 2| by utilizing accordance with standard practice.

The junction of the guides I I and I4 comprises a passage including an aperture in the lower broad side of the guide I I, the interior space of the box I6, and an aperture in the upper broad side of the guide I4, so that the passage provides access from the field space within the hollow guide I I to the field space within the hollow guide I4. The passage side being equal to the larger cross-sectional dimension A, Fig. 2, of the hollow guide. This is the maximum value that either side of the area can have although either or both sides can be smaller as will be explained later.

The distance from the end plate I2, Fig. 1, to

The shaft I1, Fig. 2, is parallel to the axis of guide II and bisects the area of the aperture. The shaft is journalled in two conventional choke 3 bearings l8 and 23, although it may alternatively be journalled in the single bearing l8 and terminated near but not touching the side 24 of the square aperture.

A conductive rod 26 is secured at one end to the shaft extending normal thereto in a plane midway of the transverse dimension of the wave guide M. This rod has a length such as to just clear the sides 28 and 23 of the aperture and the lower broad side 3| of the wave guide |4 when the rod is rotated by the shaft H.

The shaft acts to divide the rectangular aperture defined by the sides 24, 28, 29 and 32, Fig. 2, into two equal windows, each .of which will support microwave transmission in only the dominant mode. One window is defined by the shaft I1 and the aperture sides :24, 28 and 32, and the other window is defined by the shaft I1 and the aperture sides 24, 29 and 32.

The rod 26 when positioned to span either window, acts to interdict that window .to the transmission of microwave energy, because the rod divides the window into two equal areas, neither of which is large enough to support the applied microwave energy in any mode. A rod of this character thus serves substantially the same purpose as a solid metal shield in preventing the passage of microwave energy through the window.

When either of the windows is left open, that is, not spanned by the rod 26, that Window constitutes a longitudinal slot in a broad side of the guide H which is displaced from its longitudinal center line, the window length being equal to the dimension A and the width being less than one-half A by the amount of the radius of the shaft However, the width may be made as small as desired although the coupling coefficient will decrease with the width. Such a slot in a guide has the property of radiating microwave energy out of the guide and the discontinuity which it presents to the source can be matched out almost completely by a suitable matching device. Such a matching device is constituted by the end plate l2, which as heretofore stated is placed at a distance from the rectangular orifice mid-point departing from Xg/ by an amount sufficient to match out the impedance discontinuity.

An unspanned window can also be considered as constituting a series openingas respects the guide |4. Such a series ope ng can couple energy to the guide if the length of the opening, which lies transversely across the guide, is greater than the cutoif value of the dimension A for the applied frequency, this cutoff dimension being approximately one-half of the wavelength in free air of the applied energy. Any impedance discontinuity presented by this series opening is matched by the previously mentioned departure of the spacing of the end plate l2 from a distance of )\g/4.

When such a series opening in the broad face of a wave guide is employed to couple microwave energy into the guide, the energy is transmitted from the opening in both directions in the guide in equal amounts and in opposite phases. For example, referring to Fig. 3, if the distances B and C from the window center plane 33 to the ends I!) and 2i of guide M be made equal, the energy leaving the end l9 will have a phase exactly opposite to the phase of that leaving the end 2|.

If the rod 26 be moved to the position indicated by the dotted lines 34, the rod interdicts the window bounded by shait l8 and Z 8 so that the 4 and 32, and leaves the window open bounded by the shaft I1 and sides 24, 29 and 32 and having a center plane 36. All microwave energy applied from guide H is then coupled through the latter window to guide l4 and none is coupled through the other window. If the dimensions of the device are made such that the distance D between the center planes 33 and 36 is exactly )\g/4, then the distance E from the center plane 36 to the terminal I9 is longer than the distance B by )\g/4, phase of microwave energy arriving at L9 is retarded by the amount )\g/4. Also, the distance F from plane 36 to terminal 2| is less than the .distance C .by k i, so that the phase of microwave energy arriving at 2| is advanced by The total advance that has been effected in the phase of the one output terminal 2| relative to the other output terminal I9 is thus 7\g/2. The instantaneous phases of these terminals are thus opposed when the rod 26 is in the full-line position, and alike when the rod is in the dotted line position 34.

The device of the invention is also reversible. If two microwave energies of appropriate frequency, exactly equal in amount and exactly opposite in phase, be applied at the terminal l9 and 2|, the rod 26 being in the full-line position, the two energies add to form output energy at the end of guide that is indicated in Fig. 1 as connected to a generator. Also, if the rod is in the dotted position 34 and equal amounts of equally phased energy be applied to the terminals I9 and 2|, they will add in opposite phase at the center plane 36 and pass out the guide H, as before.

When microwave energy is transmitted through this device, the voltage standing wave ratio is found to be very low with the rod 24 in either of its two interdicting positions, but during movement of the rod from one position to the other an appreciable mismatch will occur. However, less mismatch will occur as indicated by reflection into the guide 1|, when that guide is used as the input arm, if the motion of the arm 24 is downward as indicated by the are 31, rather than in the .opposite direction.

If the dimension D is not equal precisely to )\g/4 the relative phase change at the terminals |9 and 2| will not be exactly )\g/2, or but will be proportional to the distance D, or the phase change in degrees will equal 720 D divided In order to make the phase change an exact reversal or 180, D must equal A /i, being measured always between the center planes 33 and 36. The distance between these planes can be reduced by reducing the distance between the sides 28 and 29 of the box l6, Fig. 2, and can be increased by increasing the diameter of the shaft i1. By manipulation of either or both of these variables, which can be done within wide limits without materially affecting the efficiency of the device, the dimension D can be made exactly equal to )vg/ or to any other value desired that is not too far removed therefrom.

What is claimed is:

1. A microwave phase shifter comprising, first and second rectangular wave guide sections positioned in overlapped relation with their broad faces in parallel planes and their axes in planes normal to each other to form a T junction, a communicating aperture in adjacent broad faces of said wave guide sections forming an energy transmission path therebetween, said aperture having a length in a direction transverse to said second wave guide section such that the full length thereof will transmit microwave energy While substantially less than the :full length thereof will prevent the transmission of such energy in any mode, a reflective termination for one end of said first wave guide section, and conductive means selectively positioned to intersaid aperture by dividing said one-half or the other half width into two portions, the lengths of each of which are insufficient to support the transmission of microwave energy.

2. A microwave phase shifter comprising, first and second rectangular wave guide sections p0- sitioned in overlapped relation with their broad faces in parallel planes and their axes in planes normal to each other to form a T junction, a communicating aperture in adjacent broad faces of said wave guide sections forming an energy transmission path therebetween, said aperture having a length in a direction transverse to said second wave guide section such that the full length thereof will transmit microwave energy while substantially less than the full length thereof will prevent the transmission of such energy in any mode, one end of said first wave guide section being reflectively terminated, a rotatable shaft parallel to said first Wave guide and dividing said aperture into two equal windows, and a rod secured to said shaft and extending normal thereto to partly bisect one or the other of said Windows in accordance with the rotatable positioning of said shaft.

3. A microwave phase shifter comprising, first and second rectangular wave guide sections positioned in overlapped relation with their broad faces in parallel planes and their axes in planes normal to each other to form a T junction, communicating aperture means in adjacent broad or the other half of the width of or the other of said winwith the rotatable positionto partly bisect one dows in accordance ing of said shaft.

4. A microwave with claim 3 in which the maximum dimensions References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,396,044 Fox Mar. 5, 1946 2,602,859 Moreno July 8, 1952 OTHER REFERENCES Microwave Transmission Circuits, edited by Ragan, vol. 9 of the Radiation Laboratory Series.

Published by McGraW-Hill May 21, 1948, page,

536, Copy in Div. 69, 

